Conventionally, use of ultrasonic actuators has been attempted in various mobile apparatuses. Ultrasonic actuators are usually configured using a vibrating member provided with a piezoelectric device which is an electromechanical energy conversion device, and a driven member (moving member) that contacts the vibrating member in a state in which it is pressed against the vibrating member. An ultrasonic actuator causes relative movement due to frictional force between the driven member which is pressure contacted with the vibrating member when an elliptical vibration (hereinafter includes a circular vibration) of a part of the vibrating member is caused by an expansion and contraction movement of the vibrating member upon input of a driving signal to the vibrating member.
Since an ultrasonic actuator has a small size and has excellent low noise characteristics, and since it is possible to carry out high speed and high accuracy position control, it has come to be used as the driving device in electronic equipment such as electronic cameras, etc., and its applications are still expanding.
On the other hand, in recent years, along with the progress in size reduction and higher performance of electronic equipment, there has been a demand for still higher performance in the drive capability of ultrasonic actuators used as the driving device of electronic equipment.
Thus, in order to meet such requirements, various investigations have been made to increase the driving efficiency of ultrasonic actuators.
For example, a rotational drive type ultrasonic actuator is known (see Japanese Unexamined Patent Application Publication No. H08-322270) which is provided with an equilateral triangle shaped piezoelectric vibrating element with an electrode divided into two pieces by the line connecting one of the vertices which serve as a point of contact with the moving member and the middle point of its opposite side, where elliptical vibration is excited at the vertex that becomes the point of contact, thereby frictional drive of the moving member is caused. Further, an ultrasonic motor is known (see Japanese Unexamined Patent Application Publication No. 2000-152671) in which a rotor is supported and driven rotationally using a plurality of ultrasonic vibrating elements.
The piezoelectric vibrating element disclosed in Japanese Unexamined Patent Application Publication No. H08-322270 is exciting elliptical vibration at its contact point contacted with the moving member by exciting and synthesizing vertical vibration and secondary bending vibration mode. However, in the drive method using such a vibration mode, the desired elliptical vibration is only excited at the contact point, and the other vertices vibrate following the desired elliptical vibration, and their elliptical locus and direction of rotation are different from the vertex contacted with the moving member, whereby there will be drive loss when the other vertices are contacted with the moving member. Therefore, when driving the internal peripheral surface of the rotor (the moving member), the vibrating member need to be contacted with the rotor at a single contact point, whereby the center of rotation does not get fixed with the single contact point, and a member that holds the rotor such as a bearing will be needed. Because of this, there were problems that the drive efficiency decreases due to the drive loss caused by the bearing load, as well as making the structure complex and increasing the cost.
Further, since the ultrasonic motor disclosed in Japanese Unexamined Patent Application Publication No. 2000-152671 requires a plurality of ultrasonic vibrating elements, there are problems that the structure becomes complex and the cost increases.